Indoor photovoltaics (iPVs) are emerging as a key technology to power the growing Internet of Things (IoT) market. Key iPV requirements include low-cost, safe, eco-friendly materials, high efficiency under ambient light, attractive aesthetics, and compatibility with flexible electronics. Dye-sensitized solar cells (DSSCs) meet these requirements, making them promising for indoor energy harvesting [1].

Among DSSC architectures, monolithic DSSCs (M-DSSCs), which use a single transparent conductive oxide (TCO) layer substrate, offer significant advantages over conventional sandwich-type devices. By eliminating one TCO substrate, M-DSSCs reduce material costs by ~25%, enable roll-to-roll manufacturing, simplify encapsulation, and facilitate module fabrication, enhancing their potential for large-scale production [2].

In this work, monolithic DSSC modules were fabricated on thin TCO substrates (≈1.1 mm), in place of  conventional 2.2 mm-thick TCO substrates, to facilitate integration into commercial electronics. The 10×5 cm² modules comprise a mesoporous TiO₂ photoanode, a TiO₂-rutile insulating layer, a PEDOT counter electrode, and a copper-based polymer gel electrolyte prepared by photoinduced polymerization [3], using poly(ethylene glycol) methyl ether methacrylate (PEGMA) as the monomer, and bisphenol A ethoxylate dimethacrylate (BEMA) as the crosslinking agent (1:1 wt.), with 3 wt% Irgacure® 1173 as the radical photoinitiator.

The five-cell series-connected module exhibited an open-circuit potential difference (V_OC) of 3.6 V, a short-circuit current density (J_SC) of 13.3 μA cm^-2, a maximum power point (MPP) of 23.9 μW cm^‑2, and a fill factor (ρ_FF) of 0.49, corresponding to a power conversion efficiency (ρ_PCE) of 7.5 % under 1000 lx indoor illumination (3.22 W m^-2, 2700 K LED, 60 W). To achieve output potential differences above 5 V without increasing the module footprint, each cell was laser-patterned into two electrically isolated sub-cells. The resulting ten-cell module delivered a V_OC of 7.3 V, a J_SC of 5.5 μA cm^-2, an MPP of 22.7 μW cm^‑2, an ρ_FF of 0.57, and a ρ_PCE of 8.1 %, under the same illumination conditions.

These results demonstrate that monolithic DSSC modules can deliver the output voltages required to charge low-power electronic devices while offering a scalable architecture for future IoT applications. Although further improvements in photocurrent are needed to achieve charging rates suitable for practical implementation, current efforts are directed toward fabricating these DSSC modules on ultrathin (200 μm) TCO substrates, paving the way for their integration into next-generation flexible and portable electronic devices.